Wire ropes are used as running ropes and mooring ropes. FIG. 7 shows a conventionally typical steel wire rope used for running ropes and mooring ropes. The steel wire rope 50 includes an IWRC (Independent Wire Rope Core) 51 arranged at the center thereof and six steel side strands 52 formed in a manner laid around the IWRC 51. The IWRC 51 is formed by laying seven steel strands 53.
U.S. Pat. No. 4,887,422 discloses a hybrid rope including not an IWRC 51 but rather a fiber rope arranged at the center thereof and multiple steel strands laid around the fiber rope. Fiber ropes are lighter than IWRCs and therefore the hybrid rope is lighter than steel wire ropes.
Generally in fiber ropes, the ratio of the tensile strength of a fiber rope to the tensile strength of a filament (a single fiber or a line element) included in the fiber rope (strength use efficiency) is low. That is, the tensile strength of a fiber rope formed by laying many fiber filaments is lower than the tensile strength of one of the fiber filaments. For this reason, using not an IWRC but rather a fiber rope may result in that the tensile strength does not reach that of steel wire ropes of the same diameter including an IWRC.